1. Field of the Invention
The present invention relates to multi-hop networks. The present invention is particularly suitable for applications where an autonomous ad hoc wireless network is formed by a number of wireless nodes.
2. Description of the Related Art
In a prior art multi-hop network, a message is segmented into a plurality of packets of a predetermined size and transmitted to a transit node where the packets are placed in a queue waiting to be served in a first-in-first-out basis. If QoS (quality of service) parameter is specified for an application, packets are queued according to the priority of their QoS parameter to guarantee the specified quality of the application.
Since packets are processed at each transit node of the network, the packet size and the processing delay are the determining factors of the throughput T of the network, which is determined by a traffic size (packet call size) SC divided by the latency, i.e., the time required for all packets to travel from a source to a destination. Specifically, the latency is a sum of the time required for the source to send all packets except the last one and the time required for the last packet to travel from the source to the destination, as given by (m−1) Sp/R+H·Sp/R, where m is the total number of packets, Sp, the packet size, H, the hop count number, and R is the link speed. If the delay time D is involved for processing a packet in each node, the overall latency is equal to (m−1)Sp/R+H·Sp/R+(H−1)D and the throughput T is given by T=Sc/{(m−1)Sp/R+H·Sp/R+(H−1)D}, indicating that throughput is variable as a function of packet size.
Assuming that the traffic size is modeled by a truncated Pareto distributed random variable producing a mean traffic size of 25 Kbytes (shape parameter α=1.1 and scale parameter k=4.5 Kbytes, see 3rd Generation Partnership Project (3GPP), Technical Specification Group Radio Access Network, Physical Layer Aspects of UTRA High Speed Downlink Packet Access, Release 2000), and that no processing delays are involved, the throughput of the prior art multi-hop network varies as a function of packet size, as depicted in FIG. 1A. Therefore, a multi-hop network of the type where the packet size is fixed is not capable of guaranteeing maximum throughput for all hop count numbers, resulting in a “throughput gap” among routes of different hop count numbers.
If the packet size and link speed are maintained constant at 300 Octets and 100 Mbps, respectively, the throughput of the prior art network varies as a function of the processing delay as shown in FIG. 1B. Thus, the packet size that maximizes throughput varies with hop count numbers. In terms of transmission and processing delays, the prior art multi-hop wireless network also produces a “throughput gap” among routes of different hop count numbers. This problem is serious for high hop-count routes because of their large transmission and processing delays.